Abstract

In this thesis, several factors which affect the channel capacity of multi-input multi-output communication systems have been studied under the assumption of a narrow-band Rayleigh fading channel. The first factor is the capacity's diversity property. The previously known result is verified that the outage (a certain probability is out) capacity of N1 transmit antennas and N 2 receive antennas systems is higher than that of N 2 transmit antennas and N1 receive antennas when they have the same signal-to-noise ratio and N 1 < N2 in the independent and identically distributed Rayleigh fading channel. The second is the point of diminishing returns in the increase of capacity with the increase of the number of antennas. With the Monte Carlo simulation, it is found that six receive antennas reach the point of capacity diminishing returns for a small number of transmit antennas and four transmit antennas reach the point for a small number of receive antennas. The third is the correlation between different paths in a correlated narrow-band Rayleigh fading channel. It is shown that the receive antenna polarization matrix must be orthogonal with the incident source polarization matrix to achieve zero correlation. An abstract spherical model is introduced so that the effect of antenna pattern on the correlation and thus the capacity can be studied. It is found that the broadside linear array with the half-wave square patch microstrip antennas has higher outage capacity than that with half-wave dipole antennas in most orientations. This phenomenon still exists when both the transmit array and the receive array are square and rectangular arrays, respectively. Furthermore, a correlation model based on a statistical Student's t-distribution of angle-of-arrival is developed in order to investigate the effect of antenna pattern in a more realistic environment. It was found that the vertical linear array with half-wave patch microstrip elements has higher capacity than that with half-wave dipole elements in the orientation of the antenna visible region. However, for the horizontal linear array, the microstrip elements have different variation of capacity versus orientation with the dipole elements due to the effect of antenna pattern. The cross linear array illustrates higher capacity than the vertical and horizontal linear arrays, indicating that this array is closer to the condition of zero correlation.